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"There is a bit of a controversy about whether you should stretch at all," says Dallas trainer Ron Incerta.

When USA Track & Field conducted a clinical trial of almost 3,000 runners, the results, published last month, were essentially a wash: Those who stretched had the same injury risk as those who didn't.

A Nebraska Wesleyan University study deflated another theory, the idea that flexibility achieved through stretching makes for a better runner. The results showed that runners with tighter muscles are more economical runners -- that is, they use oxygen more efficiently -- than those who are more flexible.

"If you want to stretch because you're tight and think you'll become more flexible, I don't see that as the case," says Plano physical therapist Jake Spivey. "Stretching isn't to improve the length of the tissue, but to prepare the tissue for exercise and not create injury during the course of it. If you just take off, you can create overuse issues such as tendonitis or bursitis."

What does work best? It's a matter, Incerta says, of "dynamic vs. static stretching."

Two kinds

A quick lesson here. Dynamic stretching is basically a foreshadowing of the workout to come: arms in circles if you're a swimmer, for instance; walking or skipping if you're a runner; maybe doing knee lifts for other movements.

Static, on the other hand, involves held poses: leaning over an outstretched leg or bending toward the ground for 30 seconds or so.

Until February, triathlete Brett Skyllingstad began his workouts with traditional static stretches. Then he did some research and learned that muscles aren't ready for such movement before a workout. Now for 10 minutes before he begins, he focuses on knee lifts, side steps and leg swings. His post-workout stretches are what his beforehand stretches once were, holding positions for 30 seconds or so.

"I've noticed a huge difference," says Skyllingstad, 26, project manager for a construction company and triathlon coach for Texas Triple Threat. "I don't start out feeling flat or have that normal 10 minutes of feeling crummy or awkward. It gets your blood moving and flowing, and your heart rate more elevated."

That gradually increased blood flow is necessary for a successful workout, says Dr. Cindy Trowbridge, associate professor of kinesiology at the University of Texas at Arlington.

Warming up with dynamic stretches starts the blood moving from organs to muscles, says physical therapist Spivey, whose practice is SportsCare and Rehabilitation.

"You're getting the blood flowing, which improves the pliability of the tendon and muscle," says Spivey, who does dynamic stretching for 10 minutes before a workout and static for 10 afterward. "You're getting your heart rate elevated enough so blood is getting to the tissue, whether you're skipping, doing a lateral shuffle or high knees."

Many amateurs, whether running, biking or swimming, just take off and start going, he continues. "They think, 'I'm healthy now!' But if you just take off, you can create overuse issues such as tendonitis or bursitis. It takes longer to strengthen muscles and joints than it does to strengthen your cardiovascular system."

Incerta likens the warming-up process to starting a car in the middle of winter.

"It won't run as efficiently if it's been sitting in 30-degree weather," he says. "The gears aren't going to shift right. But if you turn it on and warm it up for 10 to 15 minutes, it will be fine. Fluids are going through the pipes. No problems. It's similar to the central nervous system of the body. If you're not primed, you're not ready to actually do physical work. Warming up gets all that fluid going."

Cooling down

On the other side of the workout is when Trowbridge advocates the stretching that we tend to think of when we hear the word. You're telling your body the workout is over, she says. You are allowing it to rest, to start repairing itself from this workout and to start preparing itself for the next one.

"You've been dramatically active," she says. "It's important to bring the body back down. You don't put a kid who just had cotton candy to bed right away. You read a story. So after you exercise, you have to quiet down, to cool down. Your muscles are moderately fatigued and more responsive to being elongated or stretched because they're so warm. It's like putting cold taffy in the microwave."